Evidence exists for the association between attention-deficit hyperactivity disorder (ADHD) and possible structural,1-12 functional11,13-20 and neurotransmitter21-30 alterations in various regions of the brain in children, adolescents and adults with ADHD.

Childhood/Adolescent ADHD and the brain by Dr Mitul Mehta

Adult ADHD and the brain by Dr Mitul Mehta and Prof Philip Asherson

Having watched these two videos on “ADHD and the brain”, would you use them in consultation with your patients to demonstrate that ADHD may be a life-long disease?

Yes

No

N/A

Structural

Imaging studies suggest that ADHD is typically associated with some structural abnormalities in the brain.

The following structural abnormalities have been observed in children/adolescents and adults with ADHD versus healthy controls:

Cortical maturation in patients with and without ADHD. Reproduced with kind permission.9

Rate of cortical maturation in patients with and without ADHD. Reproduced with kind permission.9

A prospective follow-up study, which compared MRI brain scans of adults with ADHD and adults without ADHD (n=59 and n=80, respectively), found that adults with ADHD had significantly lower mean surface-wide cortical thickness and regional grey matter density (p<0.001) compared with adults without ADHD.1

The bilateral dorsal network was affected by these structural changes (found in the parietal, temporal and posterior frontal regions), and the researchers concluded that this supported previous evidence of the involvement of this region in attention functioning (Figure).1

These findings support the work of the first study of cortical thickness in adults with ADHD, which compared MRI scans of adults with ADHD with scans of adults without ADHD (n=24 and n=18, respectively) and found that adults with ADHD had significant thinning in the cortical neural network associated with attention, which primarily involved the right frontal and parietal lobes, compared with adults without ADHD (p=0.034).11

Neurobiological correlates of adult ADHD

Functional neuroimaging studies have identified under- or over-activation of some brain networks in adults with ADHD compared with healthy controls.14-16

One meta-analysis of 16 functional MRI studies of adults with and without ADHD demonstrated that the patterns of under- and over-activation differed significantly between these groups of patients. Networks under-activated in ADHD were almost exclusively located in the frontoparietal network, whereas over-activated regions were found in the visual, dorsal attention and default mode networks.14
Furthermore, the overall distribution of under- and over-activation differed significantly between networks, indicating that the pathology of ADHD may be based upon the interrelationships between networks.14

Polymorphisms in the serotonin transporter gene have been associated with differential response to ADHD treatment27 and the presence of comorbid conduct disorder in children and adolescents with hyperkinetic disorder.30

In adults with ADHD, deficiencies in glutamate signalling may play a role in modulating neurotransmitter release in some brain regions.25,26

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